Washington — For the first time since the Reagan administration came to power, the Pentagon is truly on the defensive regarding its multibillion-dollar budget.
President Reagan reaffirmed his goal of increasing defense spending in a speech he delivered Tuesday in New Orleans.
But key Republicans and business groups around the country say the defense buildup must be slowed in the name of economic recovery. A new Harris poll conducted for Business Week shows a ''massive public defection from the goal of ever-higher defense spending.'' The conservative Heritage Foundation and the usually pro-defense Wall Street Journal point to sloppy Pentagon management and questionable weapons systems.
One key reason for this heightened concern: Not only does the Reagan administration want to spend a lot more money, but its weapons-buying plan would also mean whopping bills coming due through the 1980s, impairing any attempt to reduce the federal deficit.
Within the administration, the battle again is between Defense Secretary Caspar W. Weinberger and Budget Director David A. Stockman. On Capitol Hill, the House defense appropriations subcommittee this week is working over the $214 billion 1983 Pentagon budget with an eye to significant cuts. If they don't finish during this lame duck session, the news could be even worse for the Pentagon: Three-quarters of the incoming freshman Democrats campaigned for a slowdown in defense spending.
The administration's accelerated arms-buying plan is based on political as well as military reasoning. The White House believes it must counter the steady Soviet buildup in conventional and nuclear might. But it also hoped to take advantage of earlier public support for a strengthened defense.
The ''spend-out'' rate for major weapons is lengthy compared with funds allocated for operations and maintenance. For example, Congress has to spend only 2.4 percent of the money authorized for a new ship in the first year, compared with 83 percent for operations and maintenance. Once Congress has committed the armed services to a new tank, plane, missile, or ship, however, it must pay the bigger bills coming due or cancel a weapon (which rarely happens).
The Congressional Budget Office notes that weapons procurement under the Reagan administration increases steadily and significantly as a portion of the defense budget. The Pentagon is poised to buy such ''big ticket'' items as the MX missile, two new nuclear aircraft carriers, and the B-1 bomber. Many are asking if all this new weaponry should be purchased.
Republican governors meeting in Kansas City, Mo., this week groused about their losses in this month's elections and criticized excessive military spending. Senate Budget Committee chairman Pete Domenici (R) of New Mexico said unemployment in the United States has ''reached the point where it is politically unacceptable'' and suggested that defense spending would have to be curbed to help pay for a jobs program.
In his first major speech since resigning as chief economic adviser to President Reagan, Murray Weidenbaum recently said: ''Intensive analysis should be given to the military budget. . . . There seems to be little justification for the economic feasibility of this sharply upward movement.''
Officials with the Business Roundtable, the Business Council, the American Retail Federation, and the National Association of Manufacturers told the National Journal last week that the rate of increase in defense spending should be slowed. Former President Gerald R. Ford also recently suggested stretching out the administration's defense buildup plan to reduce its economic impact.
In a recent editorial, the Wall Street Journal complained that ''the Reagan defense policy has been to throw money at the Pentagon, relying on the generals and admirals to compile the shopping lists. . . . This is a recipe for an expensive and clumsy defense apparatus.''
The Heritage Foundation (which supports an even bigger defense effort) warned in a recent report that ''the administration has almost certainly underestimated the true cost of its weapons program by at least $100 billion.'' The conservative think tank worries that ''the high cost of weapons . . . threatens to undermine the pro-defense consensus.'' But this consensus is already dissipating rapidly.
A special poll for Business Week magazine conducted by Louis Harris & Associates finds that public approval for increased defense spending has dropped from 71 percent in 1980 to 17 percent last month, ''the lowest level since 1971, when Americans were sick of the Vietnam war and sick of spending billions on it.''
Congress is unlikely to make massive cuts in defense spending for 1983. But the public and political mood now is such that a significant reduction in the rate of increase - especially in the years beyond - is now more likely.